The invention relates to a heat exchanger, in particular for controlling the temperature of batteries or electronics, having at least one header with a bottom and a top, with openings which are provided in the bottom for receiving tube ends of tubes which are in fluidic communication with the headers, the headers being formed from a U-shaped element with two parallel limbs and a bottom region which connects the limbs, the openings being provided in the bottom region and a wall region which is introduced between the limbs being provided as top.